1. Field of the Invention
The present invention relates to a color correcting relation extracting method for extracting an association relation among colors before and after color correction in the event that an original image is reproduced involving a color correction, and a color correction method for reproducing the color correction.
2. Description of the Related Art
In a technical field of printing, a photograph and the like, in the event that an original image on a reversal film is transferred onto a printing paper or a photographic paper to make a printed matter or a photograph, it often happens that an operator applies a color correction to form a high quality of image having the tone of a color, which is visually preferable for a person, on the printed matter or the photograph.
Hitherto, for forming such a high quality of image, there is use a specified system for producing a printed matter or a photograph to optimize the system in accordance with experience of an operator of the system.
For example, in case of the printing, when an original image on a reversal film is read by a scanner to derive image data, the image data is corrected through an operation of the scanner by the operator. An image is printed in accordance with the corrected image data, so that a preferable tone of color image is produced. At that time, a correction parameter for correcting the image data derived through the scanner is optimized in accordance with know-how based on the experience of an operator of the scanner, taking into consideration properties of the system in its entirety including printing papers, printing ink and the like. That is, a know-how of image formation, in which an image having a preferable tone of color is formed from an original image on a reversal film, is possessed by the operator of the scanner. Here, it is assumed that the operator of the scanner optimizes the correction parameter for a combination of a certain film and printing ink so that an image having a preferable tone of color is obtained. However, in the event that the film and/or the printing ink are replaced by other film and/or printing ink, the correction parameter will be changed to an inappropriate correction parameter. Thus, in this case, there is a need to optimize the correction parameter again.
On the other hand, in case of the photograph, a reversal film is loaded on a laboratory system and adjusted light for exposure is projected onto the loaded reversal film, so that a corrected image is obtained. The corrected image thus obtained is printed on a printing paper to form an image having a preferable tone of color. At that time, a balance among R light, G light and B light for the exposure and an exposure time are optimized by an operator of the laboratory system and an automatic control mechanism of the laboratory system, taking into consideration properties of the system in its entirety including films, a light source, printing papers and the like. Further, also with respect to a combination of a sort of a film and a sort of a printing paper, there is selected such an optimum combination that a preferable tone of color image can be obtained. That is, a know-how of image formation, in which an image having a preferable tone of color is formed, is possessed by the operator of the laboratory system, a maker of the laboratory system and a maker of the film. Here, it is assumed that an exposure time or the like is optimized for a combination of a certain film and a certain printing paper so that an image having a preferable tone of color is obtained. However, for example, in the event that the film is replaced by another film developed newly, the combination of the film and the printing paper and the exposure time will be inappropriate for the new film. Thus, also in this case, there is a need to optimize the exposure time and the like again.
Thus, in both the cases of the printing and the photograph, there is a need to do over again an optimization to form an image having a preferable tone of color, whenever a film and the like is replaced by a new type of one according to a development of products.
Further, recently, as digital technology advances, it is increased that a transfer of images is performed among different industries and media. For example, in the event that instead of distribution of printed papers, images of the printed matter appears in a home page of the internet, the image of the printed matter will be converted into an image of a television, which is not so related to the printing industry hitherto. Further, for example, it begins that one shot of an image photographed by a home video is printed out by a printer of a personal computer, or outputted on a printing paper for a photograph. In the event that such a transfer of images is performed, it is desired that a high quality of image having a preferable tone of color as mentioned above is obtained at the received end of the image. However, according to the prior art, the above-mentioned know-how is merely allowed to be used only in the individual industries such as the printing industry and the photographic industry, but is not allowed to be used in a different industry on a common basis.
In view of the foregoing, it is an object of the present invention to provide a color correcting relation extracting method capable of extracting the above-mentioned know-how, and a color correction method capable of reproducing the know-how.
To achieve the above-mentioned object, the present invention provides a color correcting relation extracting method comprising:
a measuring step of obtaining coordinate values of a colorimetry color space describing colorimetry values of a color, corresponding to a color of a reproduced image wherein an original image is formed with a color correction, through a measurement of the reproduced image; and
an obtaining step of obtaining coordinate values of the colorimetry color space corresponding to a color of the original image,
whereby an association between colors before and after the color correction is extracted.
Here, in the obtaining step, it is acceptable that colorimetry values are obtained through a colorimetry measurement of an original image, or alternatively an original image is written into a reversal film or the like in which a color characteristic is known beforehand, by means of a laser beam so as to offer a predetermined colorimetry values of color.
According to the color correcting relation extracting method of the present invention, coordinate values of the colorimetry color space corresponding to colors of the original image and the reproduced image are obtained. This feature makes it possible to extract a know-how of the color correction independent of a device for forming an original image.
In the color correcting relation extracting method according to the present, invention as mentioned above, it is acceptable that said measuring step includes a characteristic value measuring step of obtaining a characteristic value capable of being converted into the coordinate values of the colorimetry color space, corresponding to a color of the reproduced image, through measuring the reproduced image, and a first conversion step of converting the characteristic value obtained by the characteristic value measuring step into the coordinate values of the colorimetry color space.
Or alternatively, it is acceptable that said obtaining step includes a characteristic obtaining step of obtaining a characteristic values capable of being converted into the coordinate value of the colorimetry color space, corresponding to a color of the original image, and a second conversion step of converting the characteristic value obtained by the characteristic value obtaining step into the coordinate values of the colorimetry color space.
Colorimetry values of color of an image on a reversal film and a printing paper can be calculated in accordance with a characteristic value such as dye density of the reversal film or the like and a color characteristic of the reversal film or the like. Accordingly, it is possible to extract a know-how in form of device-independence in such a manner that dye density or the like of the original image and the reproduced image is derived and colorimetry values are computed from the dye density or the like thus obtained.
To achieve the above-mentioned object, the present invention provides a color correction method comprising:
a color correction conversion definition producing step including a first partial step of obtaining a coordinate values of a colorimetry color space describing colorimetry values of a color, corresponding to a color of a reproduced image wherein an original image is formed with a color correction, through a measurement of the reproduced image, and a second partial step of obtaining coordinate values of the colorimetry color space corresponding to a color of the original image, whereby said color correction conversion definition producing step produces a color correction conversion definition defining an association between coordinate values of the colorimetry color space corresponding to colors before and after the color correction;
a first device conversion step of using a conversion definition according to characteristics of image receipt or image output by a first device for receiving an image to obtain image data or outputting an image based on image data, to convert coordinate values in a first color space describing image data for the first device into coordinate values of the colorimetry color space independent of the device;
a color correction conversion step of using the color correction conversion definition produced in said color correction conversion definition producing step to convert coordinate values of the colorimetry color space corresponding to a color before the color correction into coordinate values of the colorimetry color space corresponding to a color after the color correction; and
a second device conversion step of using a conversion definition according to characteristics of image receipt or image output by a second device for receiving an image to obtain image data or outputting an image based on image data, to convert coordinate values of the colorimetry color space into coordinate values in a second color space describing image data for the second device,
whereby the image data defined by the first color space is converted into image data defined by the second color space, said image data being representative of an image in which the color correction is applied to an image based on the image data defined by the first color space.
Here, it is acceptable that the respective steps of the first device conversion step, the color correction conversion step and the second device conversion step are sequentially carried out in the named order, or alternately they are carried out in form of a united conversion process in which those steps are united.
According to the color correction method according to the present invention, in the color correction conversion definition producing step, there is produced a color correction conversion definition corresponding to a know-how extracted independent of a device for forming an original. And in the image data conversion step, the color correction conversion definition is used to convert the image data. This feature makes it possible to reproduce the color correction regardless of the sort of a device for forming an original image.
In the color correction method according to the present invention as mentioned above, it is acceptable that said color correction conversion definition producing step produces, as said color correction conversion definition, a color correction conversion definition defining an association between coordinate values within an area of original image colors reproducible as colors of the original image of the colorimetry color space and coordinate values within an area of reproduced image colors reproducible as colors of the reproduced image of the colorimetry color space,
before execution of the color correction conversion step, there is carried out a first gamut conversion step in which coordinate values within an area of colors reproducible as colors of an image received or outputted by the first device of the colorimetry color space are converted into coordinate values within an area of the original image colors, and
after execution of the color correction conversion step, there is carried out a second gamut conversion step in which coordinate values within an area of the reproduced image colors are converted into coordinate values within an area of colors reproducible as colors of an image received or outputted by the second device of the colorimetry color space.
Or alternatively it is acceptable that said color correction conversion definition producing step produces, as said color correction conversion definition, a color correction conversion definition defining an association between coordinate values within a predetermined area of the colorimetry color space,
before execution of the color correction conversion step, there is carried out a first gamut conversion step in which coordinate values within an area of colors reproducible as colors of an image received or outputted by the first device of the colorimetry color space are converted into the coordinate values within the predetermined area, and
after execution of the color correction conversion step, there is carried out a second gamut conversion step in which the coordinate values within predetermined area are converted into coordinate values within an area of colors reproducible as colors of an image received or outputted by the second device of the colorimetry color space.
The adoption of the gamut conversion steps makes it possible to reproduce the know-how of the color correction so that the color reproducing ability of the first device and the second device are sufficiently derived.